Modernize Mutex

- Based on C++11's `mutex`
- No more need to allocate-deallocate or check for null
- No pointer anymore, just a member variable
- Platform-specific implementations no longer needed
- Simpler for `NO_THREADS`
- `BinaryMutex` added for special cases as the non-recursive version
- `MutexLock` now takes a reference. At this point the cases of null `Mutex`es are rare. If you ever need that, just don't use `MutexLock`.
- `ScopedMutexLock` is dropped and replaced by `MutexLock`, because they were pretty much the same.

editor/editor_resource_preview.cpp

@@ -109,7 +109,7 @@ void EditorResourcePreview::_thread_func(void *ud) {
 
 void EditorResourcePreview::_preview_ready(const String &p_str, const Ref<Texture> &p_texture, const Ref<Texture> &p_small_texture, ObjectID id, const StringName &p_func, const Variant &p_ud) {
 
-	preview_mutex->lock();
+	preview_mutex.lock();
 
 	String path = p_str;
 	uint32_t hash = 0;
@@ -131,7 +131,7 @@ void EditorResourcePreview::_preview_ready(const String &p_str, const Ref<Textur
 
 	cache[path] = item;
 
-	preview_mutex->unlock();
+	preview_mutex.unlock();
 
 	MessageQueue::get_singleton()->push_call(id, p_func, path, p_texture, p_small_texture, p_ud);
 }
@@ -221,7 +221,7 @@ void EditorResourcePreview::_thread() {
 	while (!exit) {
 
 		preview_sem->wait();
-		preview_mutex->lock();
+		preview_mutex.lock();
 
 		if (queue.size()) {
 
@@ -237,10 +237,10 @@ void EditorResourcePreview::_thread() {
 
 				_preview_ready(path, cache[item.path].preview, cache[item.path].small_preview, item.id, item.function, item.userdata);
 
-				preview_mutex->unlock();
+				preview_mutex.unlock();
 			} else {
 
-				preview_mutex->unlock();
+				preview_mutex.unlock();
 
 				Ref<ImageTexture> texture;
 				Ref<ImageTexture> small_texture;
@@ -347,7 +347,7 @@ void EditorResourcePreview::_thread() {
 			}
 
 		} else {
-			preview_mutex->unlock();
+			preview_mutex.unlock();
 		}
 	}
 	exited = true;
@@ -358,7 +358,7 @@ void EditorResourcePreview::queue_edited_resource_preview(const Ref<Resource> &p
 	ERR_FAIL_NULL(p_receiver);
 	ERR_FAIL_COND(!p_res.is_valid());
 
-	preview_mutex->lock();
+	preview_mutex.lock();
 
 	String path_id = "ID:" + itos(p_res->get_instance_id());
 
@@ -366,7 +366,7 @@ void EditorResourcePreview::queue_edited_resource_preview(const Ref<Resource> &p
 
 		cache[path_id].order = order++;
 		p_receiver->call(p_receiver_func, path_id, cache[path_id].preview, cache[path_id].small_preview, p_userdata);
-		preview_mutex->unlock();
+		preview_mutex.unlock();
 		return;
 	}
 
@@ -380,18 +380,18 @@ void EditorResourcePreview::queue_edited_resource_preview(const Ref<Resource> &p
 	item.userdata = p_userdata;
 
 	queue.push_back(item);
-	preview_mutex->unlock();
+	preview_mutex.unlock();
 	preview_sem->post();
 }
 
 void EditorResourcePreview::queue_resource_preview(const String &p_path, Object *p_receiver, const StringName &p_receiver_func, const Variant &p_userdata) {
 
 	ERR_FAIL_NULL(p_receiver);
-	preview_mutex->lock();
+	preview_mutex.lock();
 	if (cache.has(p_path)) {
 		cache[p_path].order = order++;
 		p_receiver->call(p_receiver_func, p_path, cache[p_path].preview, cache[p_path].small_preview, p_userdata);
-		preview_mutex->unlock();
+		preview_mutex.unlock();
 		return;
 	}
 
@@ -402,7 +402,7 @@ void EditorResourcePreview::queue_resource_preview(const String &p_path, Object
 	item.userdata = p_userdata;
 
 	queue.push_back(item);
-	preview_mutex->unlock();
+	preview_mutex.unlock();
 	preview_sem->post();
 }
 
@@ -436,7 +436,7 @@ void EditorResourcePreview::_bind_methods() {
 
 void EditorResourcePreview::check_for_invalidation(const String &p_path) {
 
-	preview_mutex->lock();
+	preview_mutex.lock();
 
 	bool call_invalidated = false;
 	if (cache.has(p_path)) {
@@ -448,7 +448,7 @@ void EditorResourcePreview::check_for_invalidation(const String &p_path) {
 		}
 	}
 
-	preview_mutex->unlock();
+	preview_mutex.unlock();
 
 	if (call_invalidated) { //do outside mutex
 		call_deferred("emit_signal", "preview_invalidated", p_path);
@@ -477,7 +477,6 @@ void EditorResourcePreview::stop() {
 EditorResourcePreview::EditorResourcePreview() {
 	thread = NULL;
 	singleton = this;
-	preview_mutex = Mutex::create();
 	preview_sem = Semaphore::create();
 	order = 0;
 	exit = false;
@@ -487,6 +486,5 @@ EditorResourcePreview::EditorResourcePreview() {
 EditorResourcePreview::~EditorResourcePreview() {
 
 	stop();
-	memdelete(preview_mutex);
 	memdelete(preview_sem);
 }